A conventional cam shaft support structure used for a car internal combustion engine is disclosed in Japanese Unexamined Patent Publication No. 2005-90696, for example. Referring to FIG. 50, the cam shaft support structure described in the document comprises a cam shaft 201 having a cam lobe 201a, a cylindrical journal part 201b supported by a roller bearing 202, and an end large diameter part 201c, a housing comprising a cylinder head 208 and a cap 209, and the roller bearing 202 including a plurality of rollers 203, roughly semi-cylindrical retainers 204 and 205, and roughly semi-cylindrical race plates 206 and 207, and supporting the cam shaft 201 rotatably with respect to the housing.
Here, the outer diameter dimension of the journal part 201b is smaller than the maximum dimension of the outer diameter of the cam lobe 201a and the outer diameter dimension of the end large diameter part 201c. Therefore, the roller bearing 202 to be arranged at the journal part 201b to support the cam shaft 201 rotatably cannot be inserted from the axial direction of the cam shaft 201.
Thus, the roller bearing 202 has the plurality of rollers 203, the circumferentially split roughly semi-cylindrical retainers 204 and 205, and the circumferentially split roughly semi-cylindrical race plates 206 and 207 arranged between the cylinder head 208 and the cap 209. In addition, referring to FIG. 51, the race plate 207 has two projections 207a projecting from the circumferential each end to the radial outer side, and the cap 209 has recessions 209a corresponding to the projections 207a. 
Thus, according to the document, when the projections 207a engages with the recessions 209a, the relative movement between the race plate 207 and the cap 209 is prevented in the circumferential direction and an axial direction during the rotation of the roller bearing 202. In addition, the same is true on the space between the race plate 206 and the cylinder head 208.
The race plates 206 and 207 having the above constitution are produced by pressing a steel plate such as cold rolled steel plate (SPC) in general. In addition, a heat treatment is performed in order to obtain predetermined mechanical properties such as hardness after the predetermined configuration is provided.
According to the roller bearing 202 disclosed in the above document, the projection 207a is formed by applying force in the direction of radial outer side from the inner diameter surface of the race plate 207 so that the outer diameter surface thereof is protruded. As a result, a recession is formed in the inner diameter surface of the race plate 207 serving as a track surface of the roller 203, which causes vibration to be generated when the roller 203 passes through the recession, and the surface of the roller 203 to be removed in an early stage, so that the smooth rotation of the roller 203 is hindered.
Furthermore, although the roller bearing 202 rotates with lubricant oil supplied from an oil pump (not shown) set outside, the lubricant oil is discharged from the space between the cam shaft 201 and the race plates 206 and 207 in large amounts. Meanwhile, as the oil pump has been required to be miniaturized recently, the lubricant oil could not be supplied to the roller bearing 202 sufficiently.
In addition, this problem arises in not only the roller bearing supporting the cam shaft, but also a bearing supporting the crank shaft and the rocker shaft.
In addition, according to an assembling method of the above cam shaft support structure, the race plate 206, the retainer 204 previously provided with the rollers 203, the cam shaft 201, the retainer 203, the race plate 207 and the cap 209 are assembled in this order onto the cylinder head 208, and finally, the cylinder head 208 and the cap 209 are fastened by a bolt and the like in general.
Here, since the race plates 206 and 207 and the retainers 204 and 205 are not fixed to any part during the assembling operation, when these are shifted in position or fall, the assembling operation has to be started all over again. This problem is especially serious in the cam shaft support structure of an engine having many cylinders.